Comparison of capillary electrophoresis and isoelectric focusing for analysis of casein/caseinate addition in processed cheeses

Capillary electrophoresis (CE) and immobilized pH gradient isoelectric focusing were applied for the determination of the addition of isoelectric casein, rennet casein and sodium caseinate to processed cheeses of known composition containing different dairy products. Both methods allowed the determination of these protein ingredients by analysing the intact κ-CN. The comparison of the quantitative determination by both techniques demonstrated that they presented similar recoveries for isoelectric casein, but for sodium caseinate, a considerably better recovery was obtained by using the isoelectric focusing method (85.6% versus 47.2%). However, CE showed higher precision. CE was applied for the determination of the addition of rennet casein by the use of a calibration curve calculated by plotting the peak area ratio ∑β-CN A/para-κ-CN in the electropherograms versus the content of rennet casein of known composition cheeses from the same manufacture batch. This approach gave recoveries of added rennet casein between 94% and 102%.